Use of equine pericardium sheet (LYOMESH®) as dura mater substitute in endoscopic endonasal transsphenoidal surgery.

OBJECTIVE
The aim of this study was to describe the use of equine pericardium sheet (Lyomesh (®) ) as dural substitute for sellar reconstruction after endoscopic endonasal transsphenoidal surgery for the removal of pituitary adenomas.


METHODS
We reviewed data of patients that underwent surgery by means of an endoscopic endonasal transsphenoidal approach for the removal of pituitary adenomas over a 12-months period, starting in May 2012, i.e. when we adopted Lyomesh (®) (Audio Technologies, Piacenza, Italy) an equine pericardium sheet, as dura mater substitute.


RESULTS
During the 12-months period evaluated, we performed an endoscopic endonasal transsphenoidal operation for a variety of pituitary lesions on 102 consecutive patients. Among these, in 12 patients (9.4%) harboring a pituitary adenoma, the implant of the pericardium sheet was used. Four patients (33.3%) presented a small intraoperative cerebrospinal fluid (CSF) leak; in these cases the Lyomesh (®) was placed intradurally with fibrin glue and, thereafter, several layers were positioned in extradural space. In 8 other subjects without any evidence of CSF leak, the dural substitute was placed intradurally and fibrin glue was injected intradurally to hold the material in place.


CONCLUSIONS
Even if based on a relatively small patient series, our experience demonstrated that the use of equine pericardium sheet (Lyomesh (®) ) as dura mater substitute in transsphenoidal surgery is safe and biocompatible, as compared with other dural substitutes.


INTRODUCTION
The widespread use of the endoscopic techniques has widened the possibilities of the transsphenoidal surgery, providing access to several areas of the skull base. Notwithstanding a consistent number of advantages, still there are several drawbacks, among those the postoperative CSF leakage. It has to be minded that this risk is different between so called "standard" procedures, targeted to the sellar area and the "extended" procedures, targeted mostly to the whole midline sku ll base. Indeed, in recent series reporting outcomes of the transsphenoidal approach, either endoscopic or microscopic, for the removal o f sellar or intra-suprasellar in fradiaphrag matic lesions, the rate of postoperative CSF leak is low, ranging fro m 0% to 5.1%; on the other side, in the so called "extended" procedures this rate is higher, ranging fro m 0% to 21% [1][2][3][4][5][6][7][8][9][10][11][12]. Several d ifferent prediction factors have been identified, such as elevated BM I (body mass index) that could directly correlate with the occurrence of CSF leakage [13], although it stands clear that the ineffective repair of an intraoperative CSF fistula could be assumed as the major cause of such postoperative complications. Furthermore, the postoperative CSF leakage, if untreated, could create a direct communicat ion between nasal cavities, and the brain, thus resulting in men ingitis [2,6,14,15]. As well, the loss of CSF could lead to a tension pneumocephalus, representing another potentially devastating complicat ion of this type of 24 Università degli Studi di Salerno surgery, occurring with lower rates, usually lesser than 0.5% [16][17][18]. Therefore, in recent years, different sellar and skull base reconstruction techniques have been described, accounting on an extreme variety of strategies and materials, i.e. autologous, heterologous and synthetic. There is not a univocal consensus concerning the best reconstruction option and strategies and materials should be tailored according to every single case. The use of autologous materials (fat, muscle, fascia lata) might be preferred, because they are vital and do not engender any immune and/or inflammatory response. However, many of these substances require a separate surgical incision, either on the abdomen or on the thigh. With the modern min imally invasive conceptual way of thinking and the reduction of morb idity and mortality, the patients' requests are leant toward the avoidance of a second skin incision. For these reasons, and for the possibilities offered by these products of reliable sterility, the use of non-autologous dural substitutes, both heterologous and synthetic, has received a tremendous boost. In this environment, pericardiu m-based heterologous products are becoming increasingly popular. Lyo mesh ® (Audio Technologies, Piacenza, Italy) is an equine pericardiu m memb rane, used as dural substitute, recently introduced in the market; it is made of polypeptides chains, forming the elementary fibers, interwoven and shaped as cords, then anastomosed in complanate networks. The aim of this study is to evaluate the safety and the effectiveness of this material for sellar reconstruction after a standard endoscopic endonasal approach for the removal of a pituitary adenoma.

Patient population
We retrieved data from the analysis of 102 patients that underwent surgery for p ituitary lesions, fro m May 2012 to May 2013. The Lyo mesh ® dural foil was used in 12 cases harboring a pituitary adenoma: in four o f them it was adopted to repair an intraoperative CSF leakage -grade I according to Kelly's paradig m -, whereas in eight cases to protect a thinned suprasellar cistern -grade 0 according to Kelly's paradigm [19] -. We reported the use of such dural substitute in three PRL-secreting macroadenomas, t wo A CTH-secreting macroadenomas and seven non-functioning macroadenomas. There were five males and seven females (mean age 52.5, ranging fro m 35 to 70 years). The postoperative follow-up ranged from 3 to 12 months. The technique of reconstruction was different according to the entity of leakage to the anatomical and/or lesion features.
All patients underwent a three months postoperative endoscopic endonasal exp loration of the sino-nasal cavities and a sellar M RI scan to evaluate the integration of Lyomesh ® .

Surgical technique
All patients underwent surgery by means of an endoscopic endonasal approach to sellar region for the removal of a p ituitary adenoma, according to technique already described in the main literature [20][21][22][23][24][25][26][27]. For the reconstruction phase of the standard procedure, we usually don't harvest any autologous material such as abdominal fat graft or fascia lata, nor remove the middle turbinate to be used as free mucoperichondrium flap.
In case of small intraoperative CSF weeping leak (grade I) or also to protect a thinner and/or prolapsed suprasellar cistern (grade 0) [19], we performed the repair of the osteodural defect by mean of different techniques after tumor removal. The Lyo mesh ® foil was placed intradurally in the eight cases presenting a CSF leak grade 0, when the suprasellar cistern was intact, prolapsed into the sellar cavity but thinner; fibrin glue was injected intradurally to hold the material in place. In four cases with grade 1 intraoperative CSF leak, a single layer of Lyo mesh ® was placed intradurally with fibrin g lue and, thereafter, several layers were positioned in the extradural space to ensure the watertighteness. In two cases of this latter group the sphenoid sinus was filled with fibrin glue. Manufacture and handling of the collagen foil Lyo mesh ® is a processed equine pericardiu m deproteinized with enzy matic method that preserves only purified co llageneous network. The pericardiu m foil is made up of co mplanate mu lti-layer networks, rendered thinner by machinery process. Before its use the dural substitute must be washed at least 10 minutes in 50cc physiological saline solution. A full load of sheet measures is available.

RESULTS
There were two main reasons that required the use of the dural substitute: the first one was an intraoperative CSF leak (grade I according to Kelly [19] -occurred in four cases -, while the second one was the prolapse of an intact, thinner suprasellar cistern after tu mor removal -occurred in eight cases -. When intraoperative CSF leak was evident, the dural substitute was directly placed over the leaking points and intrasellar fibrin glue was in jected [1,28]; mu ltiple layers of Lyo mesh ® were positioned in the extradural space to complete the repair o f the osteo-dural defect (Fig. 1).  When there was not any evidence of CSF leak, the pericardiu m sheet was placed over the suprasellar cistern and then supported by the intrasellar in jection of fibrin g lue [1,28]. Th ree months MRI postoperative endoscopic control and sellar M Ri showed the comp lete integration of the dural substitute ( We did not observe any adverse clinical reactions directly related with the use of the dural substitute or any post-operative CSF leak (see Table I). Università degli Studi di Salerno

DISCUSSION
Traditional reconstruction techniques used in transcranial surgery, such as dural suturing and bone flap fixat ion, are not feasible after transsphenoidal surgery so that the osteo-dural reconstruction represents a main issue of this kind of surgery, often resulting troublesome. Sellar reconstruction after transsphenoidal pituitary tumor removal it is not mandatory in all cases but it is necessary in case of intra-operative CSF leakage or in presence of conditions that potentially expose to such event, such as the prolapse of suprasellar cistern into the sellar cavity [1,28]. Although autologous materials (fat, muscle, fascia lata) might be preferred because of their bioco mpatibility and the lesser risk o f immune o r inflammatory response, they are harvested through a separate surgical incision, either on the abdomen or on the thigh that prolongs the surgical times and could be aesthetically disfiguring. On the other hand, it has to be said that, during endoscopic endonasal surgery, autologous materials could be harvested from the nasal structures i.e. middle turbinate and/or septal mucosa.
Heterologous materials, conversely, should be preferred to the synthetic ones because they are not absorbable and their inertness is still not absolute, with the possibility of causing a cell-med iated immunoallergic response [29].
Lyo mesh ® has never been studied before for the use in this type of surgery. Thanks to the data collected along our series we have drawn some considerations in regards: 1. Watertightness: it provides a fluid-tight barrier against CSF leakage; 2. safety and biocompatibility: differently fro m bovine-derived dural substitute, this one is taken fro m horse, the only animal BSE safe, so there is no risk of infection transmission to human. It is bio logically tested, non cytotoxic, non sensitizing, non mutageneous, with zero intracutaneous reactivity. The device is biocompatible and releases molecules that are metabolized without flogistic response. Nevertheless it should be used in patients allergic to horse meat; 3. easiness to handle: can be mo lded and shaped according to different needs of the repairs; 4. transparency: the transparency of Lyo mesh ® enables the surgeon to optimally inspect the underlying tissues; 5. mechanical resistance: the sheet traction and pressure resistance indexes are far higher than the one of the collagen tissues obtained through purification and artificial reticulat ion. Lyo mesh ® shows the mechanical resistance/thickness best ratio if co mpared with other b iologic tissues of animal orig in and to the artificial co llageneous sheets; 6. slow resorption: it remains unchanged while fibroblasts and endotelial cells enter it, acting as a guide for connective regeneration while it Università degli Studi di Salerno is slowly digested and replaced by autologous connective tissue. Since no previous studies are currently availab le to assess its security and effectiveness in transsphenoidal pituitary surgery, we used this new dural substitute only in cases of small CSF weeping, to protect the suprasellar cistern after the tumor removal or to close the sellar floor. In fact, especially in cases of large or invasive adenomas, the suprasellar arachnoidal memb rane could be thinned and the diaphragma sellae could be incompetent: even if there is not intraoperative evidence of CSF leak, this latter may occur later. Therefore, in these cases, the graft was kept in place by the sole fibrin glue that has proven in preliminary studies to be sufficient for this purpose [28][29][30]. Due to the limited experience we would not yet recommend this material as sole substitute in case of large intraoperative CSF leak. In these cases, we followed the paradigm of graded sellar repair with mu ltip le materials, co mb ined to seal the d ifferent compartments of the defect [1].

CONCLUSION
Our preliminary results, even on a small patient series, demonstrate that the pericardiu m sheet, i.e. the Lyo mesh ® , presents advantages at least comparable with prev ious studies on similar materials [31]: it is safe, it is easy to handle and it is effect ive as dural substitute for the standard endoscopic procedures for pituitary adenomas removal.